帮小弟我看看用链表实现集合的交并差的C++程序哪里有错

#include <iostream>
#include <fstream>
#include <list>
using namespace std;
template<typename T>
void display(list<T> c2)
{
list <T>::iterator c2_iter;
c2_iter=c2.begin();
while (c2_iter != c2.end())
{
cout <<" "<<*c2_iter;
c2_iter++;
}
cout <<endl;
}
void jiao(list<int> a,list<int> b,list<int> c){
list<int>::iterator ita=a.begin();
list<int>::iterator itb=b.begin();
do{
do 
{
if (*ita == *itb)
{
c.push_back(*ita);
itb++;
ita++;
}else{
itb++;
}
} while (itb != b.end());
}while(ita != a.end());
}

int main()
{
list<int> a;
list<int> b;
list<int> c;
ifstream ain ("a.in");
ifstream bin ("b.in");
int at,bt;
while(ain >>at){
a.push_back(at);
}
while(bin >>bt){
b.push_back(bt);
}
display(a);
display(b);
jiao(a,b,c);
display(c);

return 0;
}

void jiao(list<int> a,list<int> b,list<int> &c) //注意是&c
{
  list<int>::iterator ita=a.begin();
  list<int>::iterator itb;
  do
  {
    itb=b.begin();
    do 
    {
      if (*ita == *itb)
      {
        c.push_back(*ita);
        break;
      }
      else
      {
        itb++;
      }
    } while (itb != b.end());
    ita++;
  }while(ita != a.end());
}